This invention relates to the field of plant husbandry and more particularly to an improved method and composition for promoting plant growth and health by enhancement of mycorrhizal infection of the plant root system. The invention also relates to the enhancement of plant development by foliar application of plant growth regulator solutions.
In order to promote plant growth in soil of low to moderate fertility, a variety of nutrients are added by fertilization, most prominently nitrogen, potassium and phosphorus. Fertilizers are also used to add various trace elements that may be important to plant development including zinc, iron, magnesium, boron, manganese, molybdenum and copper. Although nutrients are normally supplied to plants through fertilization of the soil or other growth medium, alternative techniques are known wherein nutrients are foliarly applied, i.e., to the leaves or needles of a plant. Whatever the route exployed, supply of nutrients entirely by artificial fertilization is expensive, increasingly so in view of the rapid increases in the prices of the raw materials from which fertilizers are derived.
Mycorrhizae are symbiotic associations in which a plant's secondary root system is invaded by a specific fungi during periods of active root growth. Hyphae of the fungus penetrate the roots and effectively increase the root absorptive area, which leads to increased water uptake along with increased selective absorption and accumulation of nutrients from the soil. Mycorrhizal association is so prevalent in nature that nonmycorrhizal plants represent an exception rather than the rule. Only a relatively small number of plant genera are known to develop normally in the absence of mycorrhizal involvement while others appear to be obligately dependent upon this interaction for their orderly growth and development. In the case of plant seedlings such as, for example, tree seedlings produced in artificial growth media, inoculation of the medium with mycorrhizal fungi has been known in the art for the purpose of promoting mycorrhizal infection and development of a mycorrhizal root system. The availability of inorganic ions, particularly those containing nitrogen and phosphorus, is also known to have a critical effect on mycorrhizal formation. To a lesser degree potassium is also important for this purpose.
Excess soil fertility is known to have an adverse effect on mycorrhizal development. In fact, if fertility is too great, mycorrhizal development may be eliminated. Other recognized disadvantages of excessive soil fertilization are high cost and environmental degradation.
There is thus a need in the art for methods which will provide adequate supplies of nutrients to plants without the various disadvantageous effects of high levels of soil fertilization. In the case of containerized seedlings, there is a particular need for a method which will establish mycorrhizal root systems which are important for successful outplanting.
Various studies have been made on the effect of the treatment of plants with plant growth regulators. Certain of these studies have related to the application of growth regulators both to intact plants and to freshly cut surfaces of pruned plants. Others have dealt, for example, with the application of synthetic auxins such as the potassium salt of 3-indolebutyric acid to plants by various methods, the most effective of which have been reported to be root soaking, gel dipping, and insertion of auxin-impregnated toothpicks crosswise into the root.